This is the best summary I could come up with:
Mozilla Firefox has merged Wayland fractional-scale-v1 protocol support for handling fractional scaling with the web browser on the Linux desktop.
Merged yesterday is the Wayland fractional-scale-v1 support for this fractional scaling that has been successfully tested with the KDE KWin compositor.
Unfortunately at the moment though this Wayland fractional scaling support is disabled by default: for now interested users will need to set the widget.wayland.fractional-scale.enabled preference for enjoying this fractional scaling support.
The Wayland fractional scaling support was tracked via this bug report.
It's great seeing Firefox finally supporting Wayland fractional scaling!
The fractional-scale-v1 protocol has been enjoying fairly robust support by the numerous Wayland compositors and seeing support within Google Chrome/Chromium web browser since earlier this year and also other desktop software like the MPV video player rather than being limited to integer-based scaling.
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